In the Facebook photograph, Melanie Williams, 36, can be seen smiling and shooting a thumbs up sign to the camera.
But not all is as it seems.
Because the black mark on her thumbnail, which many assumed was a bruise from slamming the digit in a door, turned out to be something a lot more dangerous.
The mother-of-three explained: "See that on my thumb? Do you know what it is?
"It's skin cancer. This grew from nothing in a matter of weeks. I thought it was just a fungal infection or a wart. Sadly not.”
She continued: “I’ve been lucky, the cancer hasn't spread and it's being removed next week along with half of my thumb.
"This may have not been the case if I'd left it and not got it checked out. I don't want your sympathy, I want more awareness. Therefore, please go and get any changes or growths on your skin checked out, please tell people around you to get checked as well.
"Don't leave it to chance or make excuses! I will be fighting fit in no time but if I'd left it, I may have been losing more than a thumb.
"So please, don't leave comments about how brave I am or how sorry you are, instead take that time to share this or tell someone they need to get checked or make that phone call to the doctors for yourself.”
Proving that she still had an amazing sense of humour, in spite of what had happened to her, Melanie added: “P.S. If anyone knows where I can get a mini hook attachment for my stubby thumb give me a shout!"
The post has already been shared 76,349 times and liked 12,721 times.
In a later update, Melanie revealed that she had undergone an operation on her thumb, but that she may need more removed than first expected.
She told her well-wishers: “I'm due to have more tests done in the next week, so will have to see where we go from there. Thank you to everyone who shared this post.
"Totally lost for words (for those who know me, this is rare) on the response it has received. I feel proud of everyone who's shared and taken note because of the awareness it's raised!
“You lot rock!!! Xxx"
According to the NHS, the most common signs of skin cancer are:
They advise: “Don’t try to diagnose yourself – if you notice any unusual or persistent changes to your skin it could be a sign of skin cancer, so go and see your doctor.
“It’s probably nothing serious, but if it is skin cancer, finding it early makes it easier to treat.”
Find out more at their website now.